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With read great interest the recent work by Kang et al published in Circulation reporting the high incidence of in-stent neoatherosclerosis, including thin-cap fibroatheroma (TCFA) after drug-eluting stent implantation identified by optical coherent tomography (OCT).1 In this publication, Kang et al reported that neoatherosclerosis was identified in 90% of drug-eluting stent restenosis lesions, with high incidence of TCFA (52%) by OCT at median follow-up of 32.2 months. However, we recently reported in an autopsy study that neoatherosclerosis occurred in only 41% of the stented lesions, even when cases were limited to 2 to 6 years after stenting.2 Although the duration of stent implantation and the lesion characteristics of the 2 cohorts are different, this discrepancy is remarkable.

From our experience of comparison between histology and OCT, we believe there are 3 plausible explanations for the discrepancy. First, OCT cannot discern the newly formed atherosclerosis within stent from the metal strut penetration into the preexisting necrotic core of underlying plaque. It is known that drug-eluting stent strut penetration into necrotic core leads to delayed arterial healing or subtle neointimal coverage,3 which might be recognized as a new lesion of TCFA with or without intimal disruption by OCT. Another possibility is accumulation of fibrin, which is frequently observed around the struts of paclitaxel-eluting stents.4 Massive fibrin accumulation is seen on OCT as a dark area without a clear border, which resembles necrotic core. Lastly, the most serious limitations of OCT analysis is foamy macrophages accumulating on the luminal surface of neointima in the stented coronary artery, which are identified in OCT as a typical appearance of a thin bright line with trailing shadows. This feature mimics the so-called OCT-derived TCFA and prevents the accurate assessment of tissues in the deeper area. Further, accumulated macrophages are fragile, easily cracked by even soft contact with wire or catheter, and will end up with discontinuation or disruption in neointimal luminal surface.

Currently, new intracoronary imaging devices utilizing backscatter of near-infrared light such as OCT are gathering clinical attention because of their great capacity for the detection of detailed vessel structures, however, observers need to interpret OCT with caution, because there are only few validation studies available to date, especially in the in-stent areas.